This invention relates to cable equalizer circuits for compensating signals being transmitted over a cable for cable attenuation losses, and in particular to an automatic cable equilizer for compensating video signals from a television camera.
In the processing of video signals developed, for example, by television cameras located at remote, or widely differing locations, it is often found that the video signal is attenuated by the cable to such an extent that a correction is required to compensate the signal for the cable attenuation. Cable losses may be generally categorized as resistive losses and capacitive or dielectric losses. The first of these, attributed to the resistance value of the cable, causes a relatively linear attenuation over the frequency range of the signal being transmitted and is generally not of significant concern. However, cable losses, attributed to the capacitance of the cable, is of major concern as its affect is to attenuate the higher frequencies of the signal being transmitted. The problem of cable attenuation of the signal is further increased where the length of the cable is varied as often occurs when switching between video sources located at varying distances from the main video processing apparatus. Since a fixed cable compensation will not satisfy the typical video cable installation, it is common practice to view the signal being received on a waveform monitor and manually switch in cable compensation circuits, which, for example, may be in the form of high frequency emphasis networks to compensate for the high frequency losses occurring in the cable.